1. Field of the Invention
The present invention relates to a rough-polishing method of a semiconductor wafer and a polishing apparatus of a semiconductor wafer.
2. Description of Related Art
In a polishing process of a semiconductor wafer, in order to average the roughness of the entire surface of a the semiconductor wafer with etching pits and the like formed during preceding (etching) process, a rough-polishing step is often conducted before final finish-polishing step. During the rough-polishing step, the surface of the semiconductor wafers undergoes one-stage polishing, or, alternatively, multi-stage polishing using different polishing slurries in accordance with the depth of the etching pits.
By the rough-polishing step, the surface of the semiconductor wafer is smoothed to a constant roughness. In the finish-polishing step, the constant surface roughness is removed to create further minute surface roughness condition (Haze).
In order to remove the surface roughness formed during the rough-polishing process by the finish polishing, considerable amount of work is necessary during the finish polishing. The surface roughness of the semiconductor wafer during the rough-polishing step is caused by transcription of polishing pad attached on a polishing table. Accordingly, by further smoothing the polishing pad during the rough-polishing step, the surface roughness of the semiconductor wafer after the rough-polishing step can be made constant.
In view of the above, it has been traditionally known to apply a seasoning process on the surface of polishing pad using a diamond grinding stone.
Alternatively, it has been proposed to gradually raise rotating speed of polishing table during rough-polishing step (see, for instance, Document: JP2000-15571 A).
However, when a seasoning process is applied before rough-polishing, since the most appropriate polishing condition for a polishing pad of which condition is constantly changing differs at each time, it is difficult to stably obtain a constant surface roughness.
Further, when a seasoning process is frequently conducted in order to stabilize the surface roughness of semiconductor wafer, productivity of the semiconductor wafer is deteriorated during polishing process.
On the other hand, when a rotating speed of a polishing table is gradually raised during rough-polishing, since polishing table is thermally expanded on account of frictional heat generated against semiconductor wafers, it becomes difficult to keep the flatness of semiconductor wafers.